Step 1
Preheat the oven to 325 degrees F (165 degrees C). Spray two 11x17-inch baking sheets with cooking spray and line with parchment paper. Spray the parchment paper with cooking spray.
Step 2
Mix cake mix flour sugar and salt in a medium bowl.
Step 3
Place water sour cream oil vanilla almond and egg whites in the bowl of a stand mixer fitted with the paddle attachment. Mix on low speed until combined; slowly add the flour mixture. Beat together on medium speed for 2 minutes.
Step 4
Pour 1/2 of the batter into each baking sheet and spread into an even thin layer.
Step 5
Bake in the preheated oven until the edges are light golden brown and the center is set 12 to 15 minutes. Cool completely on a wire rack for at least 30 minutes.
Step 6
Transfer one of the cooled cake layers along with the parchment onto a cutting board. Spread raspberry preserves over 1/2 of the cake and blueberry preserves over the other. Spread a layer of cream cheese frosting over the second cake layer; flip frosted side over the preserves. Spread remaining frosting over the top. Slide the cake on its parchment onto a cookie sheet cover with plastic wrap and freeze for 1 hour or chill overnight.
Step 7
Cut the chilled cake into 2-inch squares by first marking with a ruler. Place squares on a wire rack over a parchment lined baking sheet. Return to the fridge to chill.
Step 8
Whisk powdered sugar water corn syrup almond and vanilla together in a glass bowl.
Step 9
Fill a small sauce pot with an inch or two of water; bring to a simmer. Place sugar mixture on top of the simmering water. Whisk until icing is smooth and temperature reaches 92 degrees F (33 degrees C). Add white chocolate chips and any food coloring and stir until melted. Turn off heat but leave double boiler on the stovetop to keep icing pourable.
Step 9
Ladle the warm icing over the top of each cake square. Quickly add sprinkles; icing should set quickly since the cake is cold. Let petits fours set in the refrigerator for about 5 minutes or at room temperature for 30 minutes.